1. Field of the Invention
The present invention relates to ink jet printers, and, more particularly, to a method and apparatus for measuring the printhead gap and drop velocity in an ink jet printer.
2. Description of the Related Art
One of the major factors that contribute to the quality of printing in an ink jet printer is the printhead gap, which is defined as the distance between the printhead nozzle plate (printhead firing plane) and the top surface of the print media (media surface plane). The printhead gap plays a large role in the issues of alignment and drop pattern on the media. From printer to printer, the printhead gap can be quite different due to multiple tolerance issues in the mechanical structure of the printer.
What is needed in the art is a device for measuring the printhead gap and drop velocity.
The present invention provides a very inexpensive apparatus that can be installed in every printer to effectively measure the printhead gap and the drop velocity.
The invention comprises, in one form thereof, a method of calculating at least a component of ink drop velocity in an ink jet printer. At least one first ink drop is jetted from a printhead firing plane. It is detected when the first ink drop is a first predetermined distance away from a reference plane. The reference plane can be the media surface plane or the platen on which the media is supported when in the print zone. A first time period between the jetting and the detecting of the first ink drop is measured. At least one second ink drop is jetted from the printhead firing plane. It is detected when the second ink drop is a second predetermined distance away from the reference plane. A second time period between the jetting and the detecting of the second ink drop is measured. A difference between the first predetermined distance and the second predetermined distance is divided by a difference between the first time period and the second time period.
The invention comprises, in another form thereof, an ink jet printer including a reference plane near and parallel to a media surface plane. A first sensor detects a presence of a first ink drop at a first predetermined distance from a reference plane. The reference plane can be the media surface plane or the platen on which the media is supported when in the print zone. A second sensor detects a presence of a second ink drop at a second predetermined distance from the reference plane. A processing device calculates a velocity of the first ink drop and the second ink drop based on the first predetermined distance, the second predetermined distance, a first time period between the printhead firing the first ink drop and the first sensor sensing the first ink drop, and a second time period between the printhead firing the second ink drop and the second sensor sensing the second ink drop.
The invention comprises, in yet another form thereof, a method of determining a length of a printhead gap between a printhead and a print media surface plane in an ink jet printer. A first ink drop is jetted from a printhead firing plane. It is detected when the first ink drop is at a first location a first predetermined distance away from a reference plane. A first time period between the jetting and the detecting of the first ink drop is measured. A second ink drop is jetted from the printhead firing plane. It is detected when the second ink drop is at a second location a second predetermined distance away from the reference plane. A second time period between the jetting and the detecting of the second ink drop is measured. An ink drop velocity is calculated by dividing a difference between the first predetermined distance and the second predetermined distance by a difference between the first time period and the second time period. A detecting distance is determined by multiplying the ink drop velocity by the first time period. The length of the printhead gap is ascertained by subtracting a distance between the media surface plane and the first location from the detecting distance, or by adding the distance between the media surface plane and the first location to the detecting distance.
The invention comprises, in a further form thereof, a method of determining an ink drop speed in a jetting direction in an ink jet printer. A printhead is moved in a scanning direction. A first ink drop is jetted in the jetting direction during the moving step. When the first ink drop is at a first location is detected. A first distance traveled by the printhead between the jetting and the detecting of the first ink drop is measured. The printhead is moved in the scanning direction or a second direction substantially opposite to the scanning direction. A second ink drop is jetted in the jetting direction during the second moving step. It is detected when the second ink drop is at a second location. A second distance traveled by the printhead between the jetting and the detecting of the second ink drop is measured. The ink drop speed is calculated dependent upon the first distance, the second distance, and a distance between the first location and the second location in the jetting direction.
An advantage of the present invention is that the printhead gap and drop velocity can be easily and inexpensively measured.
Another advantage is that ink type can be determined.
Yet another advantage is that missing or malfunctioning ink jet nozzles can be detected.